1. Field of the Invention
The present invention relates generally to fueling stations for dispensing natural gas to vehicles and, more particularly, to fueling stations having the capacity to provide and dispense both compressed natural gas (CNG) and liquified natural gas (LNG) on-demand.
2. State of the Art
Natural gas is a known alternative to combustion fuels such as gasoline and diesel. Much effort has gone into the development of natural gas as an alternative combustion fuel in order to combat various drawbacks of gasoline and diesel including production costs and the subsequent emissions created by the use thereof. As is known in the art, natural gas is a cleaner burning fuel than many other combustion fuels. Additionally, natural gas is considered to be safer than gasoline or diesel since natural gas rises in the air and dissipates, rather than settling as do other combustion fuels. However, various obstacles remain which have inhibited the widespread acceptance of natural gas as a combustion fuel for use in motor vehicles.
To be used as an alternative combustion fuel, natural gas is conventionally converted into compressed natural gas (CNG) or liquified (or liquid) natural gas (LNG) for purposes of storing and transporting the fuel prior to its use. In addition to the process of converting natural gas to CNG or LNG, additional facilities and processes are often required for the intermediate storage of, and the ultimate dispensing of, the natural gas to a motor vehicle which will burn the natural gas in a combustion process.
Conventional natural gas refueling facilities are currently prohibitively expensive to build and operate as compared to conventional fueling facilities. For example, it is presently estimated that a conventional LNG refueling station costs approximately $350,000 to $1,000,000 to construct while the cost of a comparable gasoline fueling station costs approximately $50,000 to $150,000. One of the reasons for the extreme cost difference is the cost of specialized equipment used in handling, conditioning and storing LNG which is conventionally stored as a cryogenic liquid methane at a temperature of about −130° C. to −160° C. (−200° F. to −250° F.) and at a pressure of about 25 to 135 pounds per square inch absolute (psia).
An additional problem inhibiting the widespread acceptance of natural gas as a combustion fuel for motor vehicles is that, currently, some motor vehicles which have been adapted for combustion of natural gas require CNG while others require LNG thus requiring different types of fueling facilities for each. For example, LNG facilities conventionally dispense natural gas from storage tanks wherein the natural gas is already conditioned and converted to LNG. The LNG is often conventionally delivered to the storage tanks by way of tanker trucks or similar means. On the other hand, CNG facilities often draw natural gas from a pipeline or similar supply, condition the natural gas and then compress it to produce the desired end product of CNG.
Some efforts have been made to provide LNG and CNG from a single facility. For example, U.S. Pat. No. 5,505,232 to Barclay, issued Apr. 9, 1996 is directed to an integrated refueling system which produces and supplies both LNG and CNG. The disclosed system is stated to operate on a small scale producing approximately 1,000 gallons a day of liquefied or compressed fuel product. The Barclay patent teaches that a natural gas supply be subjected to passage through a regenerative purifier, so as to remove various constituents in the gas such as carbon dioxide, water, heavy hydrocarbons and odorants prior to processing the natural gas and producing either LNG or CNG. Thus, as with conventional CNG facilities, it appears that the system disclosed in the Barclay patent requires location in close proximity to a natural gas pipeline or similar feed source.
Additionally, the system disclosed in the Barclay patent requires the natural gas to be processed through a liquefier regardless of whether it is desired to produce LNG or CNG. The requirement of an on-site liquefier may unnecessarily increase the complexity and cost of constructing a natural gas refueling facility, thus keeping the facility from being a realistic alternative to a conventional gasoline fueling facility.
Another example of a combined LNG and CNG fueling facility is disclosed in U.S. Pat. No. 5,315,831 to Goode et al, issued May 31, 1994. The Goode patent discloses a fueling facility which includes a volume of LNG stored in a cryogenic tank. LNG is drawn from the storage tank and dispensed to vehicles as required. CNG is produced by drawing off a volume of the LNG from the storage tank and flowing the LNG through a high-efficiency pump and a vaporizer system, which CNG is then dispensed to a vehicle as required.
While the Goode and Barclay patents disclose integrated fileling stations which purportedly provide the capability of dispensing LNG and/or CNG, improvements to such facilities are still desired in order to make such fueling facilities efficient, practical and comparable in costs of construction and operation relative to conventional gasoline fueling facilities.
In view of the shortcomings in the art, it would be advantageous to provide an integrated fueling system which is able to dispense LNG, CNG or both on demand and which is of simple construction, provides simple, efficient operation and otherwise improves upon the current state of the art.